Help with Wittig Reactions
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Organic Chemistry › Help with Wittig Reactions
What is the final organic product of the reaction shown?
III
I
II
IV
V
Explanation
First step: esterification
Second step: reduction
Third step: neutralization
Fourth step: oxidation to aldehyde
Fifth step: alkene metathesis
All of the following are characteristics of a Wittig reaction except __________.
it results in the exclusive formation of trans double bonds
it involves the reaction of a phosphonium ylide with a carbonyl
it proceeds through a phosphaoxetane intermediate
it results in the formation of a carbon-carbon double bond
it produces a trialkylphosphine oxide or triarylphosphine oxide as a by-product
Explanation
The Wittig reaction involves the reaction of a phosphonium ylide (generated by treating a phosphonium salt with a strong base) with a ketone or aldehyde.
The reaction proceeds through a phosphaoxetane (4-membered ring containing both phosphorus and oxygen) intermediate to generate a new compound containing a carbon-carbon double bond, plus a phosphine oxide byproduct. It does not form trans double bonds exclusively; sometimes, a mixture of cis and trans isomers are obtained, and sometimes the cis isomer is the predominant product.